Cocoon-shaped Sn4+-doped ZnO nanoparticles have been synthesized by a solvothermal method using carbon microspheres as a template. The optimum doping level for photocatalysis is 3% (g. atom). Powder X-ray diffractograms show that the ZnO has a primitive hexagonal crystal structure and that doping ZnO with Sn4+ increases the unit cell lengths and the Zn–O bond lengths. Larger crystal growth along the c-axis is also observed. The measured size of the cocoon-shaped Sn4+-doped ZnO nanoparticles is larger than the mean crystallite size. Solid state impedance spectroscopy studies reveal that Sn4+-doping increases the charge transfer resistance. Doping does not significantly modify the optical band gap, but does suppress green emission. A decrease in the number of crystal defects due to oxygen vacancies is likely to be a reason for the enhanced photocatalytic properties of the cocoon-shaped Sn4+-doped ZnO nanoparticles. Doping ZnO with Sn4+ enhances the bactericidal activity as well.